Our group is involved in the long-term goal of developing a high density genetic map of the mouse. We have been using inter(sub)species crosses to generate a map consisting almost exclusively of expressed genes and pseudogenes. These genes are mapped by the analysis of the progeny of two sets of genetic crosses - an interspecies backcross and an intersubspecies backcross. DNAs from these mice have been typed for over 900 loci, about half of which have also been genetically mapped in other systems. This permits us to map newly defined genes to specific positions on the linkage map and to integrate our data into composite maps of each chromosome. These studies have resulted in the genetic mapping of several hundred new genes this year including genes encoding sodium and calcium channels, zinc finger proteins, lymphotoxin receptor, mouse BRCA1, tetranectin, macrophage inflammatory protein, IL-2 receptor subunits, and synaptotagmins. Specific map locations can be useful information since proximity to a known developmental mutation can identify such a gene as a potential candidate for the abnormal phenotype. Other studies have focused on the organization of multigene families in the mammalian genome and on the comparative linkage relationships of homologous genes in man and mouse.